Silicon optical bench OCT probe for medical imaging

ABSTRACT

An optical probe for emitting and/or receiving light within a body comprises an optical fiber that transmits and/or receives an optical signal, a silicon optical bench including a fiber groove running longitudinally that holds an optical fiber termination of the optical fiber and a reflecting surface that optically couples an endface of the optical fiber termination to a lateral side of the optical bench. The fiber groove is fabricated using silicon anisotropic etching techniques. Some examples use a housing around the optical bench that is fabricated using LIGA or other electroforming technology. A method for forming lens structure is also described that comprises forming a refractive lens in a first layer of a composite wafer material, such as SOI (silicon on insulator) wafers and forming an optical port through a backside of the composite wafer material along an optical axis of the refractive lens. The refractive lens is preferably formed using grey-scale lithography and dry etching the first layer.

RELATED APPLICATIONS

This application is a Divisional of U.S. application Ser. No.12/693,181, filed on Jan. 25, 2010, entitled “Silicon Optical Bench OCTProbe for Medical Imaging”, now U.S. Patent Publication No.: US2011/0182550 A1, which is incorporated herein by reference in itsentirety.

BACKGROUND OF THE INVENTION

Coherence analysis relies on the use of the interference phenomenabetween a reference wave and an experimental wave or between two partsof an experimental wave to measure distances and thicknesses, andcalculate indices of refraction of a sample. Optical CoherenceTomography (OCT) is one example technology that is used to performusually high-resolution cross sectional imaging. It is applied toimaging biological tissue structures, for example, on microscopic scalesin real time. Optical waves are reflected from the tissue, in vivo, exvivo or in vitro, and a computer produces images of cross sections ofthe tissue by using information on how the waves are changed uponreflection.

The original OCT imaging technique was time-domain OCT (TD-OCT), whichused a movable reference mirror in a Michelson interferometerarrangement. In order to increase performance, variants of thistechnique have been developed using two wavelengths in so-called dualband OCT systems.

In parallel, Fourier domain OCT (FD-OCT) techniques have been developed.One example uses a wavelength swept source and a single detector; it issometimes referred to as time-encoded FD-OCT (TEFD-OCT) or swept sourceOCT. Another example uses a broadband source and a spectrally resolvingdetector system and is sometimes referred to as spectrum-encoded FD-OCTor SEFD-OCT.

In scanning OCT, a light beam is focused onto the sample under test by aprobe. Returning light is combined with light from a reference arm toyield an interferogram, providing A-scan or Z axis information. Byscanning the sample relative to the probe, linear or two dimensionalscans can be used to build up a volumetric image. One specificapplication involves the scanning of arteries, such as coronaryarteries. The probe is inserted to an artery segment of interest using acatheter system. The probe is then rotated and drawn back through theartery to produce a helical scan of the inner vessel wall.

Traditionally, scanning OCT probes have been constructed from gradientrefractive index (GRIN) lens and fold mirrors. Optical fibers are usedto transmit optical signals to the probe at the distal end of thecatheter system. The GRIN lens at the end of the fiber produces acollimated or focused beam of light and focuses incoming light onto theend of the optical fiber. The fold mirror couples to the GRIN lens to aregion lateral to the probe.

SUMMARY OF THE INVENTION

In general, according to one aspect, the invention features an opticalprobe for emitting and/or receiving light within a body. The probecomprises an optical fiber that transmits and/or receives an opticalsignal, a silicon optical bench including a fiber groove runninglongitudinally that holds an optical fiber termination of the opticalfiber and a reflecting surface that optically couples an endface of theoptical fiber termination to a lateral side of the optical bench.

In embodiments, a lens structure is secured to the optical bench overthe fold mirror surface. In some cases, the lens is anamorphic.

Further, the optical bench preferably comprises a blind groove sectionhaving a depth greater than at least part of the fiber groove with adistal end of the blind groove section forming the reflecting surface,which can be flat or curved. In the case of a curved reflecting surface,the optical power provided by the curved surface can be used to avoidthe need for the lens structure.

In other aspects of embodiments, the fiber groove comprises a firstdepth section for fiber strain relief and a second depth section, theoptical fiber comprising a sheathed portion in the first depth sectionof the optical bench and a bare portion in the second depth section ofthe optical bench.

In examples, a top bench is used over the fiber groove with the opticalfiber termination being sandwiched between the top bench and the siliconoptical bench. This top bench can have a fiber groove with a first depthsection and a second depth section, a sheathed portion of the opticalfiber being located in the first depth section of the top bench and abare portion of the optical fiber being located in the second depthsection of the top bench.

A housing is preferably provided around the bench. This housingcomprises a optical port opposite the reflecting surface, through whichthe termination of the optical fiber is optically coupled to a regionlateral to the probe.

In general according to another aspect, the invention features anoptical probe for emitting and/or receiving light within a body. Theprobe comprises an optical fiber that transmits and/or receives anoptical signal, a housing that contains an optical fiber termination ofthe optical fiber, the housing comprising at least a tubular section anda cap section, in which the cap section fits in a slot in the tubularsection.

Preferably, an optical bench is provided in the slot of the tubularsection and under the cap section, the optical fiber being held betweenthe optical bench and the cap section. This cap section can comprise agroove running longitudinally on a backside, the optical fiber beingheld in the groove. An end section is useful for closing the slot at thedistal end of the housing.

In general according to another aspect, the invention features anoptical probe for emitting and/or receiving light within a body. Thisprobe comprises an optical fiber that transmits and/or receives anoptical signal and a housing that contains an optical fiber terminationof the optical fiber, the housing comprising at least an electroformedtubular section.

In general according to still another aspect, the invention features amethod for forming an optical probe for emitting and/or receiving light.This method comprises anisotropically etching wafer material to formgrooves for holding optical fibers and singulating optical benchesincluding the grooves from the wafer material.

Preferably blind grooves are formed in the wafer material, and coated tobe reflective.

In general according to another aspect, the invention features a methodfor forming an optical probe for emitting and/or receiving light. Thismethod comprises photolithographically patterning a resist layer;electroforming housings in the patterned resist layer, and insertingoptical fiber terminations into the housings.

Preferably, the step of electroforming comprises electroplating. Themethod can also include electroforming cap sections that fit into slotsin the housings along with installing optical benches in the housings,the optical fiber terminations being held on the optical benches.

The above and other features of the invention including various noveldetails of construction and combinations of parts, and other advantages,will now be more particularly described with reference to theaccompanying drawings and pointed out in the claims. It will beunderstood that the particular method and device embodying the inventionare shown by way of illustration and not as a limitation of theinvention. The principles and features of this invention may be employedin various and numerous embodiments without departing from the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, reference characters refer to the sameparts throughout the different views. The drawings are not necessarilyto scale; emphasis has instead been placed upon illustrating theprinciples of the invention. Of the drawings:

FIG. 1 shows the catheter with the probe in a lumen of a body;

FIG. 2 is a detailed view of the probe in the sheath;

FIG. 3 is a perspective view of a bench system of the probe showing atop bench prior to installation on a bottom bench;

FIG. 4 is a perspective view of the bench system of the probe with thetop bench shown in phantom installed on the bottom bench;

FIG. 5 is a schematic side plan view showing the beam being coupled to aregion lateral to the probe;

FIG. 6 is a perspective view of the probe with the bench system beinginstalled within a housing, prior to installation of the cap portion;

FIG. 7 is a perspective view of the probe with the bench system beinginstalled within the housing and the cap portion of the housinginstalled over the bench system;

FIGS. 8A and 8B are perspective views of the probe showing two variantsof a second embodiment of the housing;

FIG. 9 is a perspective view of a second embodiment of the bench systemof the probe;

FIG. 10 is a perspective view of the third embodiment housing and endsection, in an unassembled state;

FIG. 11 is a perspective view of the housing and end section, accordingto a third embodiment, in an assembled state;

FIG. 12 is a perspective view of the housing and end section, accordingto a variant of the third embodiment;

FIG. 13 is a perspective view of the probe showing a third embodiment ofthe housing with the second embodiment optical bench system;

FIGS. 14A-14C are schematic side plan views showing an electroformingmanufacturing process for the housings made using the LIGA process;

FIGS. 15A and 15B are perspective views of a wafer of lens structures,with the edge showing the lens structures in cross-section;

FIG. 16A shows the bottom optical benches prior to singulation;

FIGS. 16B and 16C show exemplary frontside etch masks for forming thebottom optical benches; and

FIG. 16D shows an exemplary backside etch mask for forming the bottomoptical benches.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 and 2 show a catheter system to which the present invention isapplicable.

A catheter 50 is inserted into a lumen 10 of a body. In one typicalexample, the lumen 10 is a blood vessel, such as a coronary or carotidartery. In the illustrated example, the catheter 50 is located within atubular and optically transmissive sheath 20 that protects the lumen. Inmore detail, the sheath is first inserted into the lumen and then thecatheter 50 is introduced within the sheath.

A probe 100 is located at the end of the catheter 50. The probe 100emits and/or receives an optical beam B in a direction that is lateralto the probe 100. The catheter 50 includes an optical fiber 52 extendinglongitudinally in the catheter 50. This transmits the light of beam B toand/or from the probe 100.

The beam B is emitted and/or collected through an optical port 110 ofthe probe 100. The beam is transmitted through the sheath 20, seereference 58. In the example of an OCT probe, the beam B is used toanalyze the refractive index profile (A-scan) in the illuminated region12 of the vessel wall 10. A complete scan of the inner wall of thevessel 10 is collected by helically scanning the probe 100 along asegment of the vessel 10. This is typically achieved by simultaneouslyrotating the probe 100, see arrow 54, while simultaneously withdrawingthe probe 100 through the segment of interest, see arrow 56. The sheathsprotect the vessel 10 during these scanning operations.

FIG. 3 shows an optical bench system 200 that is located within theprobe 100 to optically couple the optical fiber 52 to a region that islateral to the probe 100.

In more detail, the optical bench system 200 includes a top cap bench210 and a bottom bench 230. In the preferred embodiment, these benchesare fabricated from single crystal silicon or other similar material.The topographical features: V-grooves and ridges, of the bench system200 are fabricated using a lithographic process and more specificallyanisotropic etching techniques in which planes within the crystallinestructure are etched at different rates to form the desired topography.The fabrication process many times also includes isotropic etchingtechniques such as dry etching, including reactive ion etching.

The top bench 210 fits on the bottom bench 230 such that the opticalfiber 52 and especially the glass core 52C is held and clamped betweenthe top cap bench 210 and the bottom bench 230.

To secure the fiber 52, the top cap bench 210 has a first fiber V-groove212 extending in a longitudinal direction of the top cap bench 210. Asecond fiber V-groove 214 is aligned with the first fiber V-groove 212.The first V-groove 212 is deeper than the second fiber V-groove 214. Thedepth of the first V-groove 212 accommodates the optical fiber 52including the outer polymer coating. The distal portion 52C of theoptical fiber 52 is stripped of the outer coating to expose the glasscore. As a consequence, the second fiber V-groove 214 of the top capbench 210 is shallower than the first fiber V-groove 212.

On either lateral side of the second V-groove 214 are two engagingsurfaces 216. In a lateral direction between the second V-groove 214, inthe center of the top bench 210, and the engaging surfaces 216 at eitheredge of the top cap bench 210 are V-shaped ridges 215 that define thesecond V-groove 214 of the top cap bench 210.

The bottom bench 230 includes a first fiber V-groove 232. The depth ofthe first V-groove 232 of the bottom bench 230 is set to accommodate thecoated optical fiber 52 and in this way corresponds to the first fiberV-groove 212 of the top cap bench 210. A second fiber V-groove 234 ofthe bottom bench 230 is aligned with the first fiber V-groove 232 alongthe central axis of the bottom bench 230. It is shallower than the firstfiber V-groove 232 to capture the central glass core 52C of the strippedoptical fiber 52.

At the longitudinal end of the second V-groove 234 of the bottom bench230 is a blind V-groove or recess 238. In the typical embodiment, theblind V-groove 238 is deeper than the second V-groove 234 and has adepth that is similar to the first V-groove 232 of the bottom bench 230.

The blind V-groove 238 is further characterized by an end reflectingsurface 240 at the longitudinal end of the blind V-groove and oppositethe end facet or termination 52E of the optical fiber 52. In oneexample, the end reflecting surface 240 is coated with a reflectinglayer such as a metal layer of gold or silver or a thin film multilayerdielectric mirror. In one example, the end reflecting surface 240 isplanar. In another example it is curved to provide an optical power tofocus the beam onto the end facet or termination 52E of the opticalfiber 52 and/or collimate or focus the diverging beam from the end facet52E.

On either lateral side of the first fiber V-groove 232, the second fiberV-groove 234, and the blind V-groove 238 are engaging surfaces 236 ofthe bottom bench 230. Upon assembly of the top cap bench 210 on thebottom bench 230, the engaging surfaces 216 of the top bench 210 sit onthe engaging surfaces 236 of the bottom bench 230. Further, the V-shapedridges 215 that define the second V-groove 214 of the top bench 210 fitwithin the second V-groove 234 of the bottom bench 230.

This assembly, cap bench/bottom bench, clamps the uncoated portion ofthe optical fiber 52 between the second fiber V-groove 214 of the topbench 210 and the second V-groove 234 of the bottom bench 230 providingprecise alignment. The remaining matched surfaces are in close proximityand are locked in place with bonding material such as epoxy or solder.

The length of the stripped portion 52C of the optical fiber 52 is setrelative to the length of the second V-groove 234 so that the end facet52E projects slightly to the blind V-groove 238. As a result, in theexample of the optical signal being emitted from the end of the opticalfiber 52E, the signal is reflected off of the end reflecting surface 240and directed to a region lateral to the benches 210, 230.

The increase in the V-groove size towards the turning mirror or endreflecting surface 240 helps in the subsequent bonding process. The sizeincrease between the second fiber V-groove 234 and the blind V-groove238 that forms wall D functions as a “wick stop” to prevent the epoxyfrom wicking around the end 52E of the fiber 52 during the bondingprocess.

In the current embodiment, a lens structure 260 is secured to the bottomoptical bench over a portion of the blind V-groove 238 and specificallythe end reflecting surface 240. The lens structure comprises a frame 262that rests on the engaging surface 236 of the optical bench 230. Theframe 262 has a central optical port 266. A lens 264 is secured ormonolithically fabricated within this optical port 266. In the preferredembodiment, the lens 264 is a refractive anamorphic lens constructedfrom silicon or gallium phosphide and manufactured by photolithographicmethods such as grey-scale lithography and dry etching.

The lens is anamorphic to compensate for the optical power along oneaxis provided by the curvature of the sheath 20, see FIG. 1.

FIG. 4 illustrates the optical bench system in a partially assembledstate. The top bench 210 is installed on the bottom bench 230 with theoptical fiber 52 and the stripped portion 52C clamped between the topbench 210 and the bottom bench 230. The lens structure 260, however, isremoved to illustrate the end reflecting surface 240, which has atriangular shape defined by the intersections with each wall side of theblind V-groove 238.

The outer cross-sectional profile of the assembled optical bench system200 is octagonal in the illustrated embodiment. The cross-sectionprofile is fabricated by backside V-groove etches in both the bottombench 230 and the top cap bench 210 to form beveled edges when theV-grooves are used as cleave locations for singulation.

In more detail, the back side of the top cap bench 210 is characterizedby a planar backface 220 and two beveled surfaces 218 on either side ofthe backface 220. The bottom bench 230 has a planar backface 242, twobeveled surfaces 244 on either side of the backface 242 and two verticalside walls 246 that extend between the beveled surfaces 244 of thebottom bench 230 to the beveled surfaces 218 of the cap bench 210.

This octagonal profile and/or the beveled edges of the top bench (218)and bottom bench 244 approximate a circular cross-section. As a result,the bench system 200 able to be inserted into a circular bore of anouter housing with good contact with the inner walls of the bore.

FIG. 5 illustrates how end face 52E of the optical fiber 52 is coupledto the lateral portion of the probe 100.

In more detail, in one implementation, the end facet 52E of the opticalfiber 52 is cleaved or polished at an angle of between 0 and 8°, forexample, 5°, from perpendicular. The exact angle is chosen to optimizethe optical reflectivity of the fiber end face 52E and is also dependenton the use of antireflective coatings on the end face. In more detail,the fiber end face 52E is coated with a thin film multilayer dielectricantireflective coating in one implementation to further control theoptical reflectivity of the surface and allow optimization of the fiberend-face angle to favor the capabilities of the chosen fabricationmethod.

In a specific embodiment, the light exits from the optical fiber at anangle of 2.4° from horizontal. This light is transmitted to the endreflecting surface 240. With the end reflecting surface being fabricatedfrom the silicon 111 plane, an angle of between 50° and 60° is formed.The angle will be precisely 54.74° with the crystal planes but there isa tolerance to the <100> plane when the wafer is diced out of the ingot.As a result, the beam B has an angle of about 10-20°, or 17° forexample, from perpendicular as it exits the probe.

It should be noted that while this discussion is framed in the contextof the light being emitted from the fiber 52 as beam B, the principle ofoptical reciprocity applies. Thus, the same analysis also applies to thesituation where the light originates from a region lateral to the probe100 and then is coupled into the optical fiber 52 using the endreflecting surface 240.

FIGS. 6 and 7 illustrate the optical bench system 200 of the probe 100installed within an outer housing, according to a first embodiment.

In more detail, the optical bench system 200 with the optical fiber 52is inserted into a hollow tubular outer housing assembly 310. In theillustrated embodiment, the outer housing assembly 310 comes in twopieces: a tubular section 312 with a distal dome-shaped nose 314 and acap section 316. In assembly, the optical bench system 200 with theoptical fiber 52 is slid into a cylindrical bore of the tubular section312. It is typically bonded in place using an epoxy in the preferredembodiment. Then the cap section 316 is secured on to the tubularsection 312.

The octagonal cross-sectional profile of the assembled optical benchsystem 200 ensures good a mechanical interface between the cylindricalinner bore of the tubular section 312 and the optical bench system 200.

One side of the tubular section 312 is open forming a window 318. Thecap section 316 is sized to have the same cylindrical outercircumference as the tubular section 312 but is shorter in length thanthe window 318.

The assembled outer housing assembly is illustrated in FIG. 7 with thecap section 316 installed within the window 318. It leaves an opticalport 110 over the lens structure 260 of the optical bench system 200 toaccommodate transmission of the beam B.

FIGS. 8A and 8B illustrate two variants of a second embodiment of theouter housing 310. These embodiments have a smaller window section thatis sized to the optical port 110. No cap section is required, instead,only the tubular section 312 is provided. In these embodiments, thebench system 200 is slid into the tubular section 312 until the lensstructure 260 is aligned over the optical port 110.

The variants of FIGS. 8A and 8B differ in that the FIG. 8A versionincludes an epoxy port 332 in the tubular section 312. This allows anepoxy to be applied to the length of optical fiber exposed in the epoxyport 332 to improve strain relief for the fiber and ensure goodmechanical joining between the optical bench system 200, optical fiber52, and inner cylindrical bore in the tubular section 312.

FIG. 9 shows a second embodiment of the silicon optical bench system200. In this version only a single, bottom silicon optical bench 230 isused, without a top optical bench. This is embodiment is furthersimplified in that a single fiber V-groove 234 is provided, into whichthe glass core of the optical fiber is secured.

Aligned with the single fiber V-groove 234 is a blind V-groove or recess238. The blind V-groove 238 ends in the angled reflecting surface asdescribed with respect to the first embodiment. Over the angledreflecting surface is the lens structure 260 as also described in theprevious embodiment.

The outer cross-sectional profile of the assembled optical bench system200 is also octagonal. The cross-section profile is fabricated bybackside V-groove etches in both the bottom bench 230 and the lensstructure 260 to form beveled edges when the V-grooves are used ascleave locations for singulation. In more detail, The bottom bench 230has a planar backface 242, two beveled surfaces 244 on either side ofthe backface 242 and two vertical side walls 246 that extend between thebeveled surfaces 244 of the bottom bench 230 to beveled surfaces 270 oflens structure 260.

Here also, the increase in the V-groove size towards the turning mirroror end reflecting surface 240 helps in the subsequent fiber bondingprocess. The size increase between the second fiber V-groove 234 and theblind V-groove 238 that forms wall D functions as a “wick stop” toprevent the epoxy from wicking around the end of the fiber.

This second embodiment has the advantage of being much simpler inconstruction. On the other hand, since only the glass core is secured tothe optical bench system 200, there is less strain relief for theoptical fiber.

FIGS. 10-12 show a third embodiment of the outer housing 310 that iscompatible with the second embodiment of the optical bench system 200,shown in FIG. 9.

Referring to FIG. 10, in more detail, the third embodiment comprises atubular section 312. The outer surface 350 of the tubular section has agenerally cylindrical shape. The tubular section 312 has alongitudinally running slot 340. In cross-section, that longitudinallyrunning slot 340 has vertically extending sidewalls 344 at the mouth ofthe slot. It further has a horizontal flat bottom 342. Angled or theV-groove-shaped sidewalls 346 link the vertical sidewalls 344 and theflat bottom 342 in the cross-section.

An end section 330 fits within the tubular section 312 and specificallywithin the longitudinal running slot 340. An outer wall 362 of the endsection 330 forms a cylindrical section that completes the cylindricalshape of the outer housing 310 when the end section 330 is installedwithin the slot 340. The end section 330 further has vertical sidewalls364, a flat bottom 368, and angled, V-groove sides 366 that correspondto the shape of the inner walls of the slot 340.

FIG. 11 shows the third embodiment of the housing 310 with the endsection 330 installed within the slot 340 of the tubular section 312.

FIG. 12 shows a variant of the third embodiment of the housing 310. Ithas a dome shaped end section 330.

FIG. 13 shows a fully assembled probe 100, utilizing the thirdembodiment of the housing 310 and the second embodiment of the opticalbench system 200.

In more detail, the optical fiber 52 is installed within the fiberV-groove 234 of the bottom bench 230. The bottom bench 230 in turn isinstalled within the longitudinally running slot 340 of the tubularsection 312 of the housing 310. Further, at the distal end of thelongitudinally running slot 340, the end section 330 is installed withinthe slot 340.

A cap section 380 is installed in a slot 340 over at the bottom bench230. The optical fiber 52 is clamped between the cap section 380 and thebottom bench 230. The cap section 380 has a cylindrical recess 382 inits cross section that engages the top of the optical fiber 52.Additionally, vertical sections 384 of the cap section 380 engage thecorresponding vertical walls 344 of the tubular section 310. An opticalport 110 is provided in the outer housing 310 over the lens structure260 that is installed on the bottom bench 230. This port 110 is definedby a space between the cap section 380 and the end section 330 in thelongitudinal directions and by the sides of the slot 340 in the lateraldirections.

Preferably, the third embodiment of the housing 310 illustrated in FIGS.10-13 is manufactured using the LIGA or related electroforming process.LIGA is an acronym for Lithographie, Galvanoformung, Abformung(Lithography, Electroplating, and Molding, in English) that represents afabrication technology for high-aspect-ratio microstructures thatgenerally have cross-sectionally constant profile, extrusions.

FIGS. 14A-14C are cross-sectional views showing the fabrication stepsfor the outer housing 310, end section 330 and the cap section 380 usingthe electroforming process.

Specifically, as illustrated in FIG. 14A, a thick PMMA(polymethlymethacrylate) or SU-8 resist layer 414 is bonded to aseed/release layer 412 on a substrate 410.

The depth d of the resist layer 414 determines the maximum thickness ofthe subsequently manufactured extrusion portion. As a result, the depthdetermines the length of the part: outer housing 310, end section 330and the cap section 380.

FIG. 14B illustrates the next fabrication step in the outer housing 310,end section 330 and the cap section 380. Specifically, the thick resistlayer 414 is patterned by exposure to collimated x-rays in the case of aPMMA resist or ultraviolet light in the case of SU-8. Specifically, amask 416, which is either be a positive or negative mask having thedesired pattern for the structure, is placed between the radiationsource such as a synchrotron or UV light and the resist layer 414. Theresist layer 414 is then developed into the patterned layer 414A asillustrated in FIG. 14B.

FIG. 14C shows the formation of the quasi-extrusion portion of the outerhousing 310, end section 330 and the cap section 380. Specifically, inthe preferred embodiment, the quasi-extrusion portion is formed viaelectroplating onto the seed layer 412 into the photolithographicallyformed mould of the patterned resist layer 414A. The preferred platingmetal is nickel according to the present embodiment. Nickel alloys, suchas a nickel-iron alloy, are used in other embodiments. Alternativelygold or a gold alloy is used in still other embodiments. Currently,alternative metal and alloys include: silver, silver alloy, nickelcopper, nickel cobalt, gold cobalt and alloys laden with colloidal oxideparticles to pin the microstructures.

FIGS. 15A and 15B shows a wafer of lens structures including some of thelens structures in cross-section to illustrate the fabrication method ofthe lens structures 260.

In more detail, as shown in FIG. 15A, the lens structures 260 are massproduced in wafer material W. Each lens structure comprises the frame262, which has a central optical port 266. The refractive lens 264formed over the optical port 262.

The lenses 264 are fabricated from silicon or gallium phosphide and arepreferably manufactured by photolithographic methods includinggrey-scale lithography and dry etching on the frontside FS of the waferW. In other examples, the lenses are made using the CMP processdisclosed in U.S. Pat. No. 7,416,674 B2, which is incorporated herein inits entirety by this reference.

As better shown in FIG. 15B, in the preferred embodiment, the wafermaterial W is a composite wafer, preferably silicon on insulator (SOI).The lens 264 is fabricated in the device wafer material 510. A buriedoxide interlayer 512 separates the handle wafer material 514 from thedevice wafer material 510.

Handle wafer material 514 primarily functions as the frame and themechanical support for the lens structure 260. In the preferredembodiment, the handle wafer is silicon wafer, the device layer has athickness of 10-50 μm, currently 25 μm, and the buried oxide has athickness 1-4 μm, currently 2 μm. The lens etch is roughly 5 μm deep atthe deepest point.

The optical port 266 is fabricated using a backside etch into thebackside BS of the handle wafer material 514 along a center optical axis520 of the refractive lens 264. This backside etch is preferably a dryetch, reactive ion etch, that stops on a buried oxide layer 512, whichseparates the handle wafer material 514 from the device wafer material510. A wet or dry etch is then used to remove the oxide at the bottom ofthe optical port 262 to expose the backside of the lens 264. Also in thepreferred embodiment, antireflective dielectric coatings are preferablyapplied to the frontside FS and backside BS, specifically onto the lens264.

In addition to the backside antireflective coatings, metal is preferablydeposited on the backside BS to facilitate bonding to the bottom opticalbench.

Referring back to FIG. 15A, the lens structures 260 are separated in asingulation process. In the preferred embodiment, along one axis, theV-grooves 610 are formed on the front side FS of the wafer W, in betweenthe lenses 264 of the lens structures 260. These V-grooves 610 form thebevel edges 270 of the lens structures 260 on the lateral sides. The Vgrooves 610 also function as lines for cleaving the wafer to form theseparate lines of lens structures. Lateral scribe lanes LA are used toseparate the lines of lens structures 260 into individual singulatedlens structures 260. A wet or dry etch along lanes LA is used in someembodiments to facilitate singulation.

FIG. 16A illustrates the formation of the separate bottom opticalbenches 230 on a single wafer using photolithographic/anisotropicetching. Specifically, in a single wafer W, lines of optical benches 230are formed into the frontside FS of the wafer W. These optical benches230 are then singulated into individual optical benches by cleavingalong the lateral scribe lines LA and the longitudinal scribe planes LO.

FIGS. 16B and 16C illustrate exemplary etch masks FM1, FM2 for theanisotropic etches that are used to form the frontsides FS of the bottomoptical benches 230. In more detail, the etch masks are used tophotolithographically pattern a resist layer on the wafer material,which is then developed. The frontside of wafer is then exposed to atimed, wet, anisotropic etch process using buffer KOH, for example.

FIG. 16D illustrates the relationship between the backside etch mask BMand the front side edge mask FM. In more detail, on the backside BS, thebeveled edges of the bottom optical bench (see reference 244 in FIG. 4)are formed using a backside mask BM that has two exposed portions oneither side of the mask used on the front side etch FM. The backsidemask pattern BM forms to V-grooves on each lateral side that are used toform the beveled edges on the backside of the bottom optical benches.

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

What is claimed is:
 1. A method for forming an optical probe for emitting and/or receiving light, the method comprising: anisotropically etching wafer material to form grooves for holding optical fibers; singulating optical benches including the grooves from the wafer material; and inserting the optical benches into separate housings that each have an optical port through which optical fibers are optically coupled to a region lateral to the probes.
 2. A method as claimed in claim 1, further comprising forming blind grooves in the wafer material, and coating distal ends of the blind grooves to be reflective.
 3. A method as claimed in claim 2, further comprising securing a lens structure to each of the optical benches over a reflecting surface of the distal ends.
 4. A method for forming an optical probe for emitting and/or receiving light, the method comprising: anisotropically etching wafer material to form grooves for holding optical fibers, the grooves having a first depth section for fiber strain relief and a second depth section; and singulating optical benches including the grooves from the wafer material.
 5. A method as claimed in claim 1, further comprising attaching top benches over the grooves with optical fibers being sandwiched between the top benches and the optical benches.
 6. A method as claimed in claim 4, further comprising inserting the optical benches into separate housings that each have an optical port through which optical fibers are optically coupled to a region lateral to the probes.
 7. A method for forming an optical probe for emitting and/or receiving light, the method comprising: photolithographically patterning a resist layer; electroforming housings in the patterned resist layer; and inserting optical fiber terminations into the housings to be held on optical benches that are installed within the housings.
 8. A method as claimed in claim 7, wherein the step of electroforming comprises electroplating.
 9. A method for forming an optical probe for emitting and/or receiving light, the method comprising: photolithographically patterning a resist layer; electroforming housings in the patterned resist layer; inserting optical fiber terminations into the housings; and electroforming cap sections that fit into slots in the housings.
 10. A method as claimed in claim 9, further comprising installing optical benches in the housings, the optical fiber terminations being held on the optical benches.
 11. A method for forming an optical probe for emitting and/or receiving light, the method comprising: photolithographically patterning wafer material to form grooves for holding optical fibers; singulating optical benches including the grooves from the wafer material; and installing fiber endfaces in the grooves; and attaching top benches over the grooves with the optical fibers being sandwiched between the top benches and the optical benches.
 12. A method as claimed in claim 11, wherein photolithographically patterning comprises anisotropically etching wafer material to form the grooves for holding optical fibers.
 13. A method as claimed in claim 11, further comprising forming blind grooves in the wafer material, and coating distal ends of the blind grooves to be reflective.
 14. A method as claimed in claim 13, further comprising securing a lens structure to each of the optical benches over a reflecting surface of the distal ends.
 15. A method for forming an optical probe for emitting and/or receiving light, the method comprising; photolithographically patterning wafer material to form grooves for holding optical fibers; singulating optical benches including the grooves from the wafer material; and installing fiber endfaces in the grooves; and forming the grooves to each have a first depth section for fiber strain relief and a second depth section.
 16. A method for forming an optical probe for emitting and/or receiving light, the method comprising; photolithographically patterning wafer material to form grooves for holding optical fibers; singulating optical benches including the grooves from the wafer material; and installing fiber endfaces in the grooves; and inserting the optical benches into separate housings that each have an optical port through which the optical fiber is optically coupled to a region lateral to the probe.
 17. A method as claimed in claim 16, further comprising attaching top benches over the grooves with the optical fibers being sandwiched between the top benches and the optical benches. 